Figure 3. Etv6^+/RUNX1 mice with ‘second hits’ develop a pre-B acute lymphoblastic leukemia recapitulating features of the human disease.

A. Peripheral blood (PB; ×2000 magnification), spleen, bone marrow and liver (×400 magnification in upper panels and ×1000 magnification in lower panels) from a representative mouse with BCP-ALL. The presence of lymphoblasts in the peripheral blood is obvious, as is the infiltration of the spleen, bone marrow and liver (2^nd-4^th panels), with effacement of the normal cellular architecture and replacement by nucleolated blasts. B. FACS plots from the bone marrow of a representative mouse demonstrate only background Gr-1/Mac1 myeloid cells, with the majority of cells having a B220⁺/CD19⁻/sIg- phenotype in keeping with BCP-ALL. C. D-J PCR rearrangement studies (involving DQ52 and DFL/DSP genes) were performed on spleen or bone marrow gDNA of three mice with phenotypic B-ALL. Negative control was gDNA from C57BL/6J mouse kidney (known to be unrearranged), and positive control was gDNA from a C57BL/6J primary pro-B cell bone marrow culture (known to contain a lot of DJ-rearranged alleles). Sample 1 shows two different rearrangement events (DQ52-J2 and DFL/DSP-J2 rearrangements), in keeping with a clonal B-cell population with both alleles D-J recombined. Sample 2 shows both a germline band and an identical DFL/DSP-J2 band, in keeping with a clonal B-cell population with rearrangement of one allele and germline configuration of the other. Sample 3 shows an absence of recombination.